13-08-2022, 09:02 PM
(This post was last modified: 13-08-2022, 09:09 PM by Murphyv310.)
Hi Michael.
Yes 405 is AM sound and positive going video. Spacing is 3.5Mhz.
Well that was interesting. I decided to try anode modulation using the existing output transformer in reverse basically, it sounded good but needed the balancing resistors for left and right from the PC to be reduced from 180 ohms to 47. It sounds nice and I can achieve over 90% modulation. I decided to try a 1ZH18B which reduced the filament, the only thing is the output went through the roof, the G2 is now fed from a PD but to tame the output I had to massively drop the Anode volts, tapping off the filament supply before its dropped to the filaments via the resistors gives superb results, with an anode voltage of 2.8v.
These valves really amaze me!
The video output from the PC is pretty wide, obviously the video bandwidth exceeds 3Mhz I'd say by a mile and I've noticed a bit of buzz on some scenes on audio, this doesn't occur on the ITV Channel 11 modulator but it is of course broadcast standard, I'm wondering if a bit of filtering from the output of the Vision modulator would do the trick or should I add in sharp attenuation above 3Mhz from the PC output?
Yes 405 is AM sound and positive going video. Spacing is 3.5Mhz.
Well that was interesting. I decided to try anode modulation using the existing output transformer in reverse basically, it sounded good but needed the balancing resistors for left and right from the PC to be reduced from 180 ohms to 47. It sounds nice and I can achieve over 90% modulation. I decided to try a 1ZH18B which reduced the filament, the only thing is the output went through the roof, the G2 is now fed from a PD but to tame the output I had to massively drop the Anode volts, tapping off the filament supply before its dropped to the filaments via the resistors gives superb results, with an anode voltage of 2.8v.
These valves really amaze me!
The video output from the PC is pretty wide, obviously the video bandwidth exceeds 3Mhz I'd say by a mile and I've noticed a bit of buzz on some scenes on audio, this doesn't occur on the ITV Channel 11 modulator but it is of course broadcast standard, I'm wondering if a bit of filtering from the output of the Vision modulator would do the trick or should I add in sharp attenuation above 3Mhz from the PC output?
